The invention relates to an electromechanically actuatable brake.
One such brake is known from International Patent Disclosure 96/03301. To press a brake lining against a rotating brake body (brake disk, brake drum or the like), the known brake has an actuation device with a roller thread drive, which can be driven by an electric motor. Both tightening and releasing the known brake are accomplished with the electric motor. In the event of failure, such as failure of an electronic control unit of the brake during braking, to prevent residual braking moments caused by hysteresis on the part of the actuating unit from affecting the brake body, a preferably spiral restoring spring is provided in a feature of the known brake. The spiral restoring spring engages the actuating unit and drives the actuating unit to rotate along with the electric motor in the releasing direction, so that the brake lining is lifted away from the brake body.
This brake has the disadvantage that when brake pressure is being built up, the force of the restoring spring has to be overcome as well, and to that end, the electric motor has to be correspondingly larger and supplied with greater current. There is also a dynamic loss and a worsening of efficiency.
A further disadvantage is that to keep a built-up brake force constant, the electric motor has to be supplied so strongly with current that it keeps the brake lining pressed against the brake body at a constant contact pressure, counter to the force of the restoring spring, which attendant thermal problems. A further factor is that the known brake cannot be used as a parking brake, because it releases whenever it is not supplied with electric current.
Another disadvantage is that an air clearance, that is, a spacing between the brake lining and the brake body when the brake is released, increases with increasing wear of the brake linings. On the one hand, this makes an approach course of the brake lining until it contacts the brake body longer, and it also takes longer until the brake grips. The dynamic loss increases as well. Furthermore, the force necessary to overcome the force of the restoring spring increases, since the restoring spring is more severely deformed. The energy to be brought to bear by the electric motor of the actuation device for deforming the restoring spring is equivalent to the product of the deformation travel and the deformation force; that is, as the air clearance increases, it increases at least quadratically, which very considerably worsens the efficiency of the brake when the brake linings are worn.